Curious Problem Booting from Windows 10 Installation USB?

I've just created a Windows 10 installation USB using the Media Creation Tool.

I then booted it on my Windows 8.1 Pro desktop PC just to check the USB stick would boot. It booted to the first installation Windows 10 installation window as expected. I didn't want to do anything else so I just removed the USB drive and hit the PC restart button.

On restart, the PC did a chkdsk scan of drive C: and then started automatic repair for no apparent reason!

After a few minutes of watching the automatic repair rotating circle, I just powered off the PC and restarted the PC and it booted fine straight into Windows 8.1 as normal.

Why would removing the Windows 10 USB then pressing the reset button cause chkdsk to run and automatic repair to be invoked on restart?

Steve C said:

I've just created a Windows 10 installation USB using the Media Creation Tool.

I then booted it on my Windows 8.1 Pro desktop PC just to check the USB stick would boot. It booted to the first installation Windows 10 installation window as expected. I didn't want to do anything else so I just removed the USB drive and hit the PC restart button.

On restart, the PC did a chkdsk scan of drive C: and then started automatic repair for no apparent reason!

After a few minutes of watching the automatic repair rotating circle, I just powered off the PC and restarted the PC and it booted fine straight into Windows 8.1 as normal.

Why would removing the Windows 10 USB then pressing the reset button cause chkdsk to run and automatic repair to be invoked on restart?

Perhaps it had already begun rebuild boot files.
You probably should have aborted the install, closing the windows then clicking 'Yes' when prompted 'Are you sure you want to quit the installation?'
Are you booting to the USB trough the BIOS or are you opening the USB and clicking on the 'Setup.exe'?

Yes, that could be the explanation but I don't feel like repeating the experiment! I booted the Windows 10 USB stick via the BIOS and selected Boot Override to boot from the USB stick. The Gigabyte GA-Z77X-UD5H motherboard BIOS was in UEFI mode and Secure Boot was on.